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1 #include <tommath.h> |
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2 #ifdef BN_FAST_S_MP_SQR_C |
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
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4 * |
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5 * LibTomMath is a library that provides multiple-precision |
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6 * integer arithmetic as well as number theoretic functionality. |
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7 * |
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8 * The library was designed directly after the MPI library by |
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9 * Michael Fromberger but has been written from scratch with |
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10 * additional optimizations in place. |
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11 * |
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12 * The library is free for all purposes without any express |
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13 * guarantee it works. |
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14 * |
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.org |
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16 */ |
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17 |
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18 /* the jist of squaring... |
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19 * you do like mult except the offset of the tmpx [one that |
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20 * starts closer to zero] can't equal the offset of tmpy. |
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21 * So basically you set up iy like before then you min it with |
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22 * (ty-tx) so that it never happens. You double all those |
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23 * you add in the inner loop |
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24 |
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25 After that loop you do the squares and add them in. |
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26 */ |
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27 |
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28 int fast_s_mp_sqr (mp_int * a, mp_int * b) |
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29 { |
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30 int olduse, res, pa, ix, iz; |
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31 mp_digit W[MP_WARRAY], *tmpx; |
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32 mp_word W1; |
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33 |
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34 /* grow the destination as required */ |
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35 pa = a->used + a->used; |
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36 if (b->alloc < pa) { |
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37 if ((res = mp_grow (b, pa)) != MP_OKAY) { |
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38 return res; |
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39 } |
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40 } |
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41 |
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42 /* number of output digits to produce */ |
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43 W1 = 0; |
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44 for (ix = 0; ix < pa; ix++) { |
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45 int tx, ty, iy; |
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46 mp_word _W; |
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47 mp_digit *tmpy; |
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48 |
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49 /* clear counter */ |
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50 _W = 0; |
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51 |
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52 /* get offsets into the two bignums */ |
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53 ty = MIN(a->used-1, ix); |
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54 tx = ix - ty; |
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55 |
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56 /* setup temp aliases */ |
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57 tmpx = a->dp + tx; |
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58 tmpy = a->dp + ty; |
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59 |
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60 /* this is the number of times the loop will iterrate, essentially |
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61 while (tx++ < a->used && ty-- >= 0) { ... } |
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62 */ |
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63 iy = MIN(a->used-tx, ty+1); |
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64 |
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65 /* now for squaring tx can never equal ty |
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66 * we halve the distance since they approach at a rate of 2x |
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67 * and we have to round because odd cases need to be executed |
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68 */ |
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69 iy = MIN(iy, (ty-tx+1)>>1); |
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70 |
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71 /* execute loop */ |
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72 for (iz = 0; iz < iy; iz++) { |
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73 _W += ((mp_word)*tmpx++)*((mp_word)*tmpy--); |
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74 } |
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75 |
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76 /* double the inner product and add carry */ |
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77 _W = _W + _W + W1; |
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78 |
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79 /* even columns have the square term in them */ |
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80 if ((ix&1) == 0) { |
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81 _W += ((mp_word)a->dp[ix>>1])*((mp_word)a->dp[ix>>1]); |
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82 } |
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83 |
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84 /* store it */ |
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85 W[ix] = (mp_digit)(_W & MP_MASK); |
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86 |
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87 /* make next carry */ |
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88 W1 = _W >> ((mp_word)DIGIT_BIT); |
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89 } |
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90 |
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91 /* setup dest */ |
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92 olduse = b->used; |
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93 b->used = a->used+a->used; |
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94 |
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95 { |
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96 mp_digit *tmpb; |
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97 tmpb = b->dp; |
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98 for (ix = 0; ix < pa; ix++) { |
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99 *tmpb++ = W[ix] & MP_MASK; |
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100 } |
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101 |
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102 /* clear unused digits [that existed in the old copy of c] */ |
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103 for (; ix < olduse; ix++) { |
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104 *tmpb++ = 0; |
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105 } |
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106 } |
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107 mp_clamp (b); |
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108 return MP_OKAY; |
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109 } |
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110 #endif |
